observer ·noun
Definition: a person who watches what happens but has no active part in it Level: C2
政治观察员们预计选举结果会很接近。
Political ___observers are expecting the election result to be close.
联合国观察员正在仔细监测停火情况。
The UN ___observers are carefully monitoring the ceasefire situation.
在这项心理学研究中，她扮演被动观察者的角色，只做记录而不进行干预。
During the psychological study, she acted as a passive ___observer, taking notes without intervening.